added explanations

Author: benediktschwab

crates/eproj/src/lib.rs

@@ -1,5 +1,7 @@
-//! `eproj` is a crate for converting coordinates between different geospatial
-//! coordinate reference systems.
+//! `eproj` is a library for coordinate reference system transformations.
 //!
+//! It wraps the crate [proj-sys](https://github.com/georust/proj/tree/main/proj-sys) and
+//! provides full 3D coordinate projection support. The 3D support was developed for the
+//! [tyler](https://github.com/3DGI/tyler) crate and further extended.
 
 pub use eproj_core::{Coordinate3, Error, Projector, SpatialReferenceIdentifier};